The technical scope of the invention is that of processes enabling the in-flight programming of a time to trigger a projectile element form the fire control system of a weapon.
Projectiles fired from a cannon theoretically have a well-known ballistic trajectory.
However, certain non-reproducible external factors are able to influence this trajectory.
It is known that the muzzle velocity (Vo) of the projectile can vary by a few percent from one powder charge to another depending on the firing conditions, for example, temperature, consistency of the characteristics of the powder, and barrel wear. This results in deviations in the impact on the ground of the projectile, the ground impact point varying from 1 to 35 km from the firing weapon system.
The atmospheric conditions as well as the differences concerning the drag coefficient of the projectile also notably influence its trajectory.
So as to improve firing accuracy, it is known to transmit an order to correct the trajectory to the projectile.
U.S. Pat. No. 3,995,792 thus describes a projectile whose actual trajectory is measured using laser tracking means. A fire control system using this measurement computes the deviation between the actual trajectory and the theoretical trajectory and transmits corrective orders to the projectile enabling the actual trajectory to draw nearer to the theoretical trajectory.
The trajectory is corrected, for example, using boosters or steering fins.
One drawback of such a solution is its cost. In fact, the tracking of the projectile trajectory requires the implementation of powerful (and therefore expensive) means whose range extends beyond 15 km.
Such tracking means are also bulky and are difficult to implement.
Additionally, the use of laser tracking over a major part of the trajectory prejudices firing secrecy and creates the risk of making it easier for hostile forces to locate the artillery.
A fully autonomous projectile is also known which locates its own position by means of a global positioning system (GPS).
Before firing, the projectile is programmed with its theoretical trajectory and the desired ground impact point. It measures its own actual trajectory and, using suitable algorithms, controls the implementation of trajectory correcting means.
Such a projectile is extremely costly, since it integrates an electronic unit combined with a global positioning system. Moreover, the global positioning system is bulky and prejudices the on-board load capacity of the projectile.
Patent WO84/03,759 describes a device which increases the precision of artillery firing. This device implements a speedometer, a projectile tracking radar and radio transmission means.
The radar tracks the projectile over its full trajectory and a second radar monitors the position of the target. The fire control system transmits a trajectory correction order at a given time to the projectile in order to bring it closer to its target.
Such a device is costly to implement, since two radars are required; one to track the target, the other to track the projectile. Secrecy is not ensured either, since the correction order is sent far from the firing platform.